Creep behaviour of cracked steel fibre reinforced self-compacting concrete: from micro-mechanics to composite behaviour

This work presents the results of an extensive experimental program that aims to study the long-term behaviour of cracked steel fibre reinforced self-compacting concrete (SFRSCC). At the micro-level, a series of single fibre pull-out creep tests were performed, and the fibre slip was monitored as a function of time. The influence of fibre orientation angle (0, 30 and 60 degrees), as well as pre-imposed fibre slip levels 0.3 and 0.5 mm on the creep behaviour was investigated. At the composite level, prismatic specimens were extracted from a SFRSCC panel, having in consideration the concrete flow direction. The specimens were pre-cracked up to 0.3 and 0.5 mm and subjected to a sustained flexural loading. In this stage, the influence of the pre-crack level and fibre orientation on the long-term crack opening was appraised. Furthermore, instantaneous fibre pull-out tests and bending tests were performed on undamaged specimens to quantify the effects of the creep phenomenon. It was found that a higher damage level in the specimens accelerated the creep rate. Moreover, the creep performance of the SFRSCC was influenced by the fibre orientation. Finally, the assembled creep curves did not differ considerably from the instantaneous behaviours for the adopted pre-damaged levels.T his work is supported by the FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project SlabSys - HFRC - PTDC/ECM/120394/2010. Radmix and Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), Omya Comital (limestone filler), and Pegop (Fly ash). Civitest Company for the development of the Steel Fibre Reinforced Self - Compacting Concrete used in this wor

Tensile stress–crack width law for steel fibre reinforced self-compacting concrete obtained from indirect (splitting) tensile tests

In this work, the fracture mode I parameters of steel fibre reinforced self-compacting concrete (SFRSCC) were derived from the numerical simulation of indirect splitting tensile tests. The combined experimental and numerical research allowed a comparison between the stress-crack width (σ - w) relationship acquired straightforwardly from direct tensile tests, and the σ - w response derived from inverse analysis of the splitting tensile tests results. For this purpose a comprehensive nonlinear 3D finite element (FE) modeling strategy was developed. A comparison between the experimental results obtained from splitting tensile tests and the corresponding FE simulations confirmed the good accuracy of the proposed strategy to derive the σ – w for these composites. It is concluded that the post-cracking tensile laws obtained from inverse analysis provided a close relationship with the ones obtained from the experimental uniaxial tensile tests.The studies reported in this paper are part of the research project LEGOUSE (QREN, project nº 5387). This project is co-supported by FEDER through COMPETE program (“Programa Operacional Factores de Competitividade”). The materials were supplied by Radmix and Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), Omya Comital (limestone filler), and Pegop (Fly ash).The studies reported in this paper are part of the research project LEGOUSE (QREN, project nº 5387). This project is co-supported by FEDER through COMPETE program (“Programa Operacional Factores de Competitividade”). The materials were supplied by Radmix and Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), Omya Comital (limestone filler), and Pegop (Fly ash)

The influence of fibre orientation on the post-cracking tensile behaviour of steel fibre reinforced self-compacting concrete

Adding fibres to concrete provides several advantages, especially in terms of controlling the crack opening width and propagation after the cracking onset. However, distribution and orientation of the fibres toward the active crack plane are significantly important in order to maximize its benefits. Therefore, in this study, the effect of the fibre distribution and orientation on the post-cracking tensile behaviour of the steel fibre reinforced self-compacting concrete (SFRSCC) specimens is investigated. For this purpose, several cores were extracted from distinct locations of a panel and were subjected to indirect (splitting) and direct tensile tests. The local stress-crack opening relationship (σ-w) was obtained by modelling the splitting tensile test under the finite element framework and by performing an Inverse Analysis (IA) procedure. Afterwards the σ-w law obtained from IA is then compared with the one ascertained directly from the uniaxial tensile tests. Finally, the fibre distribution/orientation parameters were determined adopting an image analysis technique.Fundação para a Ciência e a Tecnologia (FCT

Mechanical performance of fibre reinforced concrete : the role of fibre distribution and orientation

Adding fibres to concrete provides several advantages, especially in terms of controlling the crack opening width after the cracking initiation of the composite. However, distribution and orientation of the fibres toward the crack plane are significantly important in order to provide the maximum benefit for controlling crack width. Therefore, in this study, the effect of the fibre distribution and orientation on the tensile behaviour of the steel fibre reinforced self-compacting concrete (SFRSCC) specimens is investigated. For this purpose, cores that are extracted from distinct locations of a panel will be subjected to indirect (splitting) and direct tensile tests. By modeling the splitting tensile test under the finite element framework and by performing an Inverse Analysis (IA), the achieved stress-crack opening relationship (σ-w) is compared with the one obtained directly from the experimental curve obtained in the direct tensile tests.Fundação para a Ciência e a Tecnologia (FCT

A two-phase material approach to model steel fibre reinforced self-compacting concrete in panels

This work presents an experimental and numerical approach to ascertain the mechanical behaviour of steel fibre reinforced self-compacting concrete in laminar structures. Four-point flexural tests were performed on prismatic specimens extracted from a SFRSCC panel; the specimens’ behaviour was then modelled under the FEM framework. SFRSCC is assumed as a two-phase material, i.e. plain concrete and discrete steel fibres. The nonlinear material behaviour of the plain matrix was simulated using 3D smeared crack model, while the fibre reinforcement mechanisms were modelled using micro-mechanical behaviour laws determined from experimental fibre pull-out tests. The good performance of the developed numerical strategy was demonstrated.FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project SlabSys-HFRC-PTDC/ECM/120394/201

Time-dependent flexural behaviour of cracked steel fibre reinforced self-compacting concrete panels

In the present work are described and discussed the results of an extensive experimental program that aims to study the long-term behaviour of cracked steel fibre reinforced self-compacting concrete, SFRSCC, applied in laminar structures. In a first stage, the influence of the initial crack opening level (wcr = 0.3 and 0.5 mm), applied stress level, fibre orientation/dispersion and distance from the casting point, on the flexural creep behaviour of SFRSCC was investigated. Moreover, in order to evaluate the effects of the creep phenomenon on the residual flexural strength, a series of monotonic tests were also executed. It was found that wcr = 0.5 mm series showed a higher creep coefficient comparing to the series with a lower initial crack opening. Furthermore, the creep performance of the SFRSCC was influenced by the orientation of the extracted prismatic specimens regarding the direction of the concrete flow within the cast panel.This work is supported by the FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project SlabSys-HFRC-PTDC/ECM/120394/2010. The authors would like to acknowledge the materials supplied by Radmix and Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), Omya Comital (limestone filler), and Pegop (Fly ash)

Assessment of fibre orientation and distribution in steel fibre reinforced self-compacting concrete panels

The benefits of adding fibres to concrete lie, mostly, in improving the post-cracking behaviour, since its ability to transfer stresses across cracked sections is substantially increased. The post-cracking strength is dependent not only on the fibre geometry, mechanical performance and fibre/matrix interface properties, but also on the fibre orientation and distribution. Previous works have shown that in self-compacting concrete matrices, there is a preferential fibre alignment according to the concrete’s flow in the fresh state. Having in mind that fibres are more efficient if they are oriented according the principal tensile stresses, a preferential fibre alignment on a certain direction could either enhance or diminish the material and the structural performance of this composite. In this paper, it is investigated the influence of the fibre orientation and distribution on the post-cracking behaviour of the steel fibre reinforced self-compacting concrete (SFRSCC). To perform this evaluation, SFRSCC panels were casted from their centre point. Two self-compacting mixtures were prepared using the same base mix proportions. For each SFRSCC panel cylindrical specimens were extracted and the post-cracking behaviour was assessed from a crack width controlled splitting tensile test

Demand Response Implementation in an Optimization Based SCADA Model Under Real-Time Pricing Schemes

Advancement of renewable energy resources, development of smart grids, and the effectiveness of demand response programs, can be considered as solutions to deal with the rising of energy consumption. However, there is no benefit if the consumers do not have enough automation infrastructure to use the facilities. Since the entire kinds of buildings have a massive portion in electricity usage, equipping them with optimization-based systems can be very effective. For this purpose, this paper proposes an optimization-based model implemented in a Supervisory Control and Data Acquisition, and Multi Agent System. This optimization model is based on power reduction of air conditioners and lighting systems of an office building with respect to the price-based demand response programs, such as real-time pricing. The proposed system utilizes several agents associated with the different distributed based controller devices in order to perform decision making locally and communicate with other agents to fulfill the overall system’s goal. In the case study of the paper, the proposed system is used in order to show the cost reduction in the energy bill of the building, while it respects the user preferences and comfort level.The present work was done and funded in the scope of the following projects: H2020 DREAM-GO Project (Marie Sklodowska-Curie grant agreement No 641794); Project GREEDI (ANI|P2020 17822); and UID/EEA/00760/2013 funded by FEDER Funds through COMPETE program and by National Funds through FCT.info:eu-repo/semantics/publishedVersio

Effect of the displacement rate and inclination angle in steel fiber pullout tests

This paper summarizes the results obtained in an experimental campaign on the effect of the displacement pullout rate and the inclination angle of the steel fiber pullout tests. For that purpose, specimens were obtained from a self-compacting concrete with a compressive strength of 86 MPa. In the experimental program, hooked-end steel fibers of 0.75 mm diameter and 60 mm length were used. Tests were executed with both hooked-end fibers, and smooth fibers obtained from the former by cutting the hooked end. For both type of fibers, their embedment length into concrete was 20 mm, and the influence of fiber inclination angle toward the load direction was investigated by adopting values of 0∘, 30∘ and 60∘. The tests were performed at displacement rates of 0.01, 0.1 and 1 mm/s. The results have shown that the peak pullout load increased with the inclination angle, in particular for the smooth series. Furthermore, higher displacement rates led to a higher energy absorption capacity for the pullout of the smooth fibers, while the energy absorption remained almost stable for hooked-end fibers.project BIA2015-68678-C2-1-R. M. Tarifa appreciates the financial support from the Department of Applied Mechanics and Project Engineering, UCLM (2018), and from the Programa propio de I+D+i de la Universidad Politécnica de Madrid para realizar estancias de investigación internacional igual o superior a un mes (2019), to do two stays at the University of Minho, Guimarães, Portugal. E. Poveda acknowledges the funding from the International Campus of Excellence CYTEMA and the University of Castilla-La Mancha, throughout Ayudas para estancias en universidades y centros de investigación en el extranjero en 2019 en el ámbito del plan propio de investigación susceptibles de cofinanciación por el Fondo Europeo de Desarrollo Regional (FEDER), Programa 010100021 to fund her stays in the University of Minho during 2018 and 2019, respectively. The authors thank the support of the Department of Civil Engineering and the Laboratory of the Structural Division (LEST), University of Minh

On the tensile properties and fracture behaviour of steel fibre reinforced self-compacting concrete laminar structures

Adding fibres to concrete provides several advantages, especially in terms of controlling the crack opening width and propagation after the cracking onset. However, distribution and orientation of the fibres toward the active crack plane are significantly important in order to maximize its benefits. Therefore, in this study, the effect of the fibre distribution and orientation on the post-cracking tensile behaviour of the steel fibre reinforced self-compacting concrete (SFRSCC) specimens is investigated. For this purpose, several cores were extracted from distinct locations of a panel and were subjected to indirect (splitting) and direct tensile tests. The local stress-crack opening relationship (σ-w) was obtained by modelling the splitting tensile test under the finite element framework and by performing an Inverse Analysis (IA) procedure. Afterwards the σ-w law obtained from IA is then compared with the one ascertained directly from the uniaxial tensile tests. Finally, the fibre distribution/orientation parameters were determined adopting an image analysis technique.Fundação para a Ciência e a Tecnologia (FCT